Effect of Nampt stable knockdown on MM cells. (A) RPMI-8226/S, MM-1S, and U266 cells were infected with either control scrambled or 5 independent lentiviral constructs expressing shRNAs targeting Nampt (RPMI8226/S: no. 1, no. 2, no. 3, no. 4, and no. 5; MM1S: no. 1 and no. 4; U266: no. 1, no. 3, and no. 4). The effect of Nampt knockdown on cell viability was assessed by MTT analysis and presented as the percentage of control cells. Data represent mean ± SD of 2 independent experiments carried out in triplicate. (B) Four days after infection, cell lysates were subjected to Western blot analysis to assess Nampt protein expression. (C) The effect of Nampt knockdown on intracellular NAD⁺ level in MM cells infected with shRNAs (scramble or targeting Nampt) was assessed by enzyme cyclic assay and normalized to protein concentrations. Cells were analyzed 5 days after transduction.